The point of tip devices is to reduce induced drag due to lift. Horizontal tail lift loads are usually rather low in cruise, slightly up, slightly down or zero. Therefore there isn't much h. tail induced drag to reduce.

Since h. tail induced drag improvement potential is low, I doubt the improvement would overcome the form drag and weight penalties that adding h. tail tip devices would entail.

[Edited 2008-01-03 12:18:34]

Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

Quoting Faro (Thread starter):Admittedly winglets would seem to be too heavy for horizonal stabilisers, but what about fences or raiked wingtips? Would they make economic sense on some of the bigger widebodies?

In addition to what OldAeroGuy said, which I agree with, why wouldn't you just expand the span? The horizontal stab isn't span limited and increasing span is the most efficient way to reduce induced drag. That's why you see gliders with huge spans, not winglets.

Quoting 2H4 (Reply 7):So why have winglets never been installed on canards? I'm thinking of the Starship, Avanti, etc. Heck, even homebuilts.

The combination of being highly-loaded and short in span seems to make them ideal candidates for winglets.

Tdscanuck has the correct answer.

Quoting Tdscanuck (Reply 3):In addition to what OldAeroGuy said, which I agree with, why wouldn't you just expand the span?

With the exception of the VariViggen, all the modern canards (fighters not included) I can think of are already high aspect ratio with relatively high spans in an attempt to minimize their induced drag. Besides, adding winglets to a canard would force you to add more wetted area to the v. tail and/or wing winglets to recover directional stability.

Sounds like a poor trade to me.

Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

Quoting OldAeroGuy (Reply 8):all the modern canards (fighters not included) I can think of are already high aspect ratio with relatively high spans in an attempt to minimize their induced drag. Besides, adding winglets to a canard would force you to add more wetted area to the v. tail and/or wing winglets to recover directional stability.

MEL, in the Beech 1900D's case, the "winglets" on the tail are there specifically to give the aircraft enough vertical stabilizer area...this was done so that a stock Beechcraft King Air 350 tail could be used and save lots of money on production costs (of course, as we all know, it's not quite stock when you have to hang "taillets" of the horizontal stab... ).

Quoting KELPkid (Reply 11): the Beech 1900D's case, the "winglets" on the tail are there specifically to give the aircraft enough vertical stabilizer area...this was done so that a stock Beechcraft King Air 350 tail could be used and save lots of money on production costs

Quoting Tdscanuck (Reply 10):Now that's interesting...I'm a bit stumped as to the aerodynamic reasoning behind that. Are there situations were a glider is span limited?

Absolutely. Any glider hoping to compete in a 15m or 18m class, for example. Probably a significant majority of single seat gliders being built have 15m wings. Those with flaps can compete in the 15m class, those without flaps can compete in the standard class (which still has a 15m wingspan limit).

There's also a 20m class for two-seaters, several one design classes (formal and otherwise), an Open class, and a couple of handicapped classes.

Quoting Rwessel (Reply 13):
Quoting Tdscanuck (Reply 10):
Now that's interesting...I'm a bit stumped as to the aerodynamic reasoning behind that. Are there situations were a glider is span limited?

Absolutely. Any glider hoping to compete in a 15m or 18m class, for example. Probably a significant majority of single seat gliders being built have 15m wings.

Fascinating! I had no idea (gliders aren't really my area of expertise, as I'm aptly demonstrating). This explains winglets on gliders perfectly...the canonical case for winglets is to reduce drag when you're span-restricted.

Quoting Tdscanuck (Reply 14):Fascinating! I had no idea (gliders aren't really my area of expertise, as I'm aptly demonstrating). This explains winglets on gliders perfectly...the canonical case for winglets is to reduce drag when you're span-restricted.

Somewhat off topic historical tidbit:

The desire for a bit more span caused quite a ruckus in the late eighties and early nineties. Before the rules were tightened up, there was a period when a large number of new composite designs with very flexible wings were first being introduced. A few builders tried to take advantage of the lack of precision and measured 15m (or whatever) for the glider in level flight (IOW, with the wings supporting 1G worth of glider), with a significant upwards bend in the wings.

Endless acrimonious debate arose over whether "15m" did, or did not, include the actions of a pair of burly wing benders.

Interestingly the rules took a bit of a compromise that did not disqualify the milder offenders (which included the vast majority of offending gliders). The nominal wingspan is now calculated with the wings in the zero G position (which means you can use stands to lift up the wing enough to make it match that shape), and you have an inch (2.5cm) of slack.

Quoting OldAeroGuy (Reply 8):Besides, adding winglets to a canard would force you to add more wetted area to the v. tail and/or wing winglets to recover directional stability.

Quite interesting then that installation of the dish for the Hawkeye did not necessitate adding any more fins to the four stabs on the Greyhound's already crowded tail? Aren't those based on the same airframe?.....

Quoting DEVILFISH (Reply 16):Quoting OldAeroGuy (Reply 8):
Besides, adding winglets to a canard would force you to add more wetted area to the v. tail and/or wing winglets to recover directional stability.

Quite interesting then that installation of the dish for the Hawkeye did not necessitate adding any more fins to the four stabs on the Greyhound's already crowded tail? Aren't those based on the same airframe?.....

And neither did the E-3A when the radome was added to the 707-320BAdv/C.

The reason appears to be the same in both cases. The center of pressure (CP) of the radome and its supports appears to be at or aft airplane CG, thus the radome and its mounting would have a neutral impact on directional stability (Hawkeye) or might even improve it (E-3A).

Adding something like floats to a Beaver requires additional v. tail area because the float CP is forward of the airplane CG. Compare a Beaver on floats to a Beaver on wheels.

You now need the additional vertical area provided by the verticals at the tips of the h. tail.

Obvioulsy, adding winglets to a canard surface would cause their CP to be in front of airplane CG. Restoring directional stability would require additional v. tail area.

Finally, the An-225 and the 747 Space Shuttle Carrier point out a different issue.

For the 747 Space Shuttle Carrier, the wake of the Shuttle lowered dynamic pressure at the v. tail, reducing its effectiveness. The verticals on the h. tail were required to restore directional stability.

The An-225, with an extensive design change, avoided the Buran wake issue by moving the v. tails out of the Buran wake.

[Edited 2008-01-05 11:56:43]

Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

Quoting DEVILFISH (Reply 16):Quite interesting then that installation of the dish for the Hawkeye did not necessitate adding any more fins to the four stabs on the Greyhound's already crowded tail? Aren't those based on the same airframe?.....

Isn't one of those four stabs not necessary, but there because it would look wierd if they left it off?